A complete conventional lead-acid battery assembly consists of the cell elements, intercell connectors, a container, a cover, vent plugs and terminal posts. A cell element is formed by stacking together alternate negative and positive plates, with separators. A plate is composed by a lead-based plate grid carrying an active material paste. Each one of the plate grids has an integral plate lug. The lugs of the negative plates in the cell element are joined together by a cast-on-strap joint. Similarly, the lugs of the positive plates in the cell element are joined together by another cast-on-strap joint.
The conventional method used to manufacture the cast-on-strap joints for lead-acid batteries comprises the steps of: assembling and alignment a plurality of negative and positive plate groups, brushing the plate lug surfaces by means of a rotating horizontal steel brush in order to eliminate lead oxide skins and active material pastes, application of a film of a liquid flux to the freshly brushed plate lug surfaces, at room temperature, by means of a rotating felt brush or by means of a flux-impregnated sponge, and plate lugs joining by the cast-on-strap process. During the latter process, the flux-impregnated plate lugs are introduced into a suitable molten lead-based alloy contained in a suitable metallic mold. Then, the plate lugs are immobilized in such position, and the cast-on-strap joints are formed by subsequent cooling and solidification of the molten alloy in the mold. The mold cavities are previously filled with molten metal either by gravity or pressurized injection.
A characteristic feature of the cell elements produced by the conventional cast-on-strap process just described is the presence of a substantial amount of porosity located mainly at the interface between the plate lugs surface and the solidified metal of the cast-on-strap joints. This porosity is easily visible in cross-sectioned cast-on-strap joints. This type of defect may result in an accelerated corrosion at the pores, with a consequent reduction in the useful life of the batteries.
In order to determine the causes of formation of porosity in the cast-on-strap joints obtained by employing the conventional cast-on-strap process, an extensive research program was conducted. The research led to the development of the present invention. It was discovered that the pores found inside the cast-on-strap joints are due mainly to the presence on the plate lugs surface of residues of lead oxides, greases, oils, active material pastes, fluxes, residual reaction products and humidity, all of which produce substantial volumes of gas on heating in contact with the molten lead-based strap alloy. Since it was observed that several of these factors act together during the conventional cast-on-strap process, it was concluded that pore-free cast-on-strap joints cannot be reproducibly produced by employing a conventional cast-on-strap machine.
Based on a process described in a previous patent application (Ser. No. 08/941,531, filed on Sep. 30, 1997), a new apparatus capable of producing pore-free cast-on-strap joints was developed. This apparatus is used to carry out a three-step cleaning and chemical activation treatment given to a plurality of plate lugs prior to their joining by the cast-on-strap process. The treatment comprises the steps of cleaning the plate lugs by a combined action of a liquid flux and ultrasonic vibration, water rinsing the plate lugs under ultrasonic vibration, and drying the plate lugs by gas blowing. Then, the cast-on-strap joints are formed according to the conventional cast-on-strap process. Since it is important to avoid the re-oxidation of the plate lug surfaces during the time between the application of a liquid flux to them and their joining by the cast-on-strap process, the duration of the intermediate rinsing and drying operations must be kept to a minimum.
The present invention relates to a gas-blowing device used in the new apparatus based on the process described in a previous patent application (Ser. No. 08/941,531, filed on Sep. 30, 1997), which is capable of producing pore-free cast-on-strap joints when coupled to a conventional cast-on-strap machine. The gas-blowing device is used to give a simultaneous final cleaning and drying to a plurality of negative and positive plate lugs immediately after water rinsing the plate lugs under ultrasonic vibration and prior to joining the plate lugs by the cast-on-strap process. It is an object of the present invention to provide a gas-blowing device to be used in the manufacture of cast-on-strap joints which reduces porosity formation.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.